Voltage-limiting device



Nov. 29, 1927. 1,651,021

I F. E. FIELD VOLTAGE LIMITING DEVICE Filed Feb. 10. 1926 2 1 EPOWER cmcun SIGNALING APPARATUS SILICON STEEL PERMALLOY lnverrfor: Frank 5.. Field UNHT FRANK E. FIELD, 01E SQMERVTLLE, ASESTGNOR Ti) BELL TELEPEGNE LABQFRATQETES, QT NEW YORK, Ell. IL, A CORJPGRATTON 01E YQBSK.

Application February to, 19%.

This invention relates tovoltage limiting devices.

An object of the invention -is to provide an improved magnetic device for limiting the power delivered from an electric circuit to a translating device.

A related object of the invention is to guard the user of a telephone receiver against shocks that might be caused by excessive currents in the receiving circuit.

Another object of the invention is to provide a protective shunt for electric circuits which will offer a relatively high impedance to voltages which are ordinarily used in the operation of the circuit, but which, when ex cessive voltages are impressed upon the circuit, will offer a low impedance path for the excess current.

There are numerous situations in the electrical arts where it is desirable to limit the voltage across a circuit. 'An example is found in the case of telephone circuits which are exposed to inductive interference by neighboring power lines operated at relatively high potentials. If the power line hecomes accidentally grounded, for example, an abnormally high potential is set up in the telephone circuit which may cause serious acoustic shock to the telephone operator;

This invention provides an improved magnetic device for limiting the potentials that,

may be impressed upon the translating device to a predetermined value regardless of the potential, due to the above and other causes, applied to the circuit to which the translating device is connected.

More specifically, the invention provides a protection transformer having a winding which is adapted to be connected across the line to be protected. The magnetic circuit of the transformer is so arranged, in accordance with the invention, that when the voltage across the line exceeds a predetermined maximum value the impedance of the transformer is decreased to provide a low impedance path for the excess current. This is accomplished by providing the transformer with a short-cir'cuited secondary Winding on a different portion of the core than the primary winding and providing the secondary portion with a magnetic shunt of material of igh permeability at low magnetizin r forces and a 10W saturating point so that this shunt normally carries most of the flux.

VULTAGE-LTBHTJING DEVICE.

aerial Filo. 82?,203.

A particular advantage of the invention is that it provides a simple and efficient device which may be applied to any existing circuit which it is desired to protect from excess voltages without otherwise altering the circuit, and requires no maintenance after in stallation.

The drawing illustrates diagrammatically a telephone circuit equipped in accordance with the invention for protecting a telephone operators receiver from excessive line potentials. While this specific circuit has been chosen for presentation in the description, the invention may, of course, be used to advantage in many other difierent types of circuits.

The drawing illustrates a telephone transmission line l which is exposed to inductive interference from an adjacent power circuit 2. The transmission line 1 is connected lo means of a transformer 3 with a switchboard circuit 4, which has connected thereto an anti-side tone operators telephone set comprising a transmitter 5 and a receiver 6 connected a well known manner to avoid side tone. The usual subscriber set repeating coil is illustrated at 'i, and resistance 8 is employed in circuit with one side of the repeating coil to balance the impedance of the in coming line. The block 9 represents the usual signaling apparatus employed by the operator. Since in circuits of this type the potentials of the outgoing ringing currents are of the order of 100 volts, a switch is usually employed to disconnect the local telephone apparatus from the line whenever ringing currents are transmitted. A' switch 10 of any suitable construction may be provided for this purpose, but is not essential to the invention.

The protection device which is provided by the inventionto prevent excessive voltages on the line 1 from being transmitted to the receiver consists of a transformer comprising magnetic core sections 11, 12 and 13. The core sections 11 and 12 are constructed of the 531110 material. which may be silicon steel or. good magnetic iron. The core section 13, however, is composed of a magnetic material having a reluctance which is much less than that of iron or silicon steel for small magnetizing forces but is much great er than that of iron or silicon steel for comparatively large magnetizing forces.

A magnetic material which fulfills these requirements, and which may therefore be used for the core sect-ion 13, is permalloy. A suitable variety of permalloy is a composition of nickel and iron in the respective pro-- portions of 78 nickel and 21 iron. The proper treatment of these alloys in order to obtain the desired properties is described in detail in a patent to G. W. Elmen, No. 1,586,884, issued June 1, 1926. While 78%% and 21%% have been mentioned as giving the proportion of the ingredients of nickel and iron to be employed in preparing the magnetic material tor the core section 13, it will be understood that the proportion may deviate from these figures and that other ingredients may be added to vary the characteristics of the alloy.

It is a property of permalloy that its permeability at very low magnetizing iorces extraordinarily high, values of the order of 6000 for zero magnetizing force being, easily obtainable whereas the corresponding value for the best grades of iron is only about 300. The value of the permeability at zero force is obtained by determining a series of values for exceedingly low forces, say of the order of .01 to .05 gauss. The results plot linearly and may be extrapolated back to the value for H=O. v

Other important qualities of this composition are its comparatively low value of magnetization when magnetically saturated and the relatively low magnetizing force required to saturate it. The maximum magnetization of a commercial grade of perinalloy containing 78%% nickel and the rest iron is about 10,500 lines per square cm, and it is nearly saturated with a magnetizing force of 1 gauss.

The several core sections are illustrated as comprising a plurality of plates or laminations, though any other suitable core construction may be employed. The joint between the lates comprising the core sections 11 and 13 is preferably interleaved in order to reduce the eilect ot' the gap in the magnetic circuit where the silicon steel or iron meets the permalloy" In the particular construction illustrated the plates comprising the core section 12 are not interleaved with the plates of the other core sections, but are stacked in a bundle which may be secured in position by means of clamping plates 1% and bolts 15 which also serve to clamp the core sections 11 and 13 together. However, either type of joint be employed, depending upon the particular requirements oi the transt'ormer.

The primary windi on the core sec-- tion 11 is connected (5 "ly across the t er" urinals of the telephone lver 6. The constants of this winding depend upon the particular requiremen posed the transformer, its impet such that its normal shunting effect across the circuit is negligible. The winding 16 is I explained.

An alternating current flowing through the primary winding 16 produces a varying magnetizing force which, in turn, sets up varying lines of magnetic induction. in the transformer core. From the above description of. the magnetic characteristics of permalloy, it will be evident that the reluctance of the permalloy core section 13 will be much less than that of core section 12 composed of silicon steel or iron for voltages at which the telephone circuit is normally operated, and hence that under such conditions practically all of the magnetic flux caused by the current in the winding 16 will pass through core sections 11 and 13.

As the voltage across the terminals of the primary winding 16 rises, the magnetizing force applied to core sections 11 and 13 increases and the permeability of core section 13 rises rapidly. The permeability of the magnetic material of core section 13 reaches its maximum at a magnetizing iorce at which the permeability of core section 12 has not nearly reached its maximum. Thus, as the voltage across the circuit increases, the reluctance of core section 13 increases rapidly causing a corresponding increase in the flux passing through core section 12.

v dince the core section 12 is provided with. a short-circuited winding 17 this increase in the tin which flows through core section 1'2 will produce an increase in the current in the .short-circuited winding. The increased current which is thus produced in the shortcircuited winding 17 produces an increase in the flux which tlows through the primary winding 16 and thus tends to lower the inipedance oi: this winding, thereby allowing a high current to be shunted through this winding. This high current will in turn produce a greater magnetizing force in the magnetic core, increase the reluctance of core n 13, still further and cause more in w through the core section'12 which will produce larger short-circuited currents l further lower the impedthe primary winding 16. At some thereby l t balance will be reached beyond which he circuit.

1 The ll be impossible to increase the voltage Q aeenoaa the transformer may be so designed that this maximum voltage is that beyond which it is desired that the voltage shall not rise.

For each particular application of the invention a special transformer may be designed to insure the proper protecting action with a minimum shunting eflect on the circuit. In general the cross-sectional area of the high permeability section of theltransformer will be much less than that of the other sections.

The invention is also susceptible of various other modifications and adaptations not specifically referred to but included within t e scope of the appended claims.

What is claimed is:

1. In combination, a line, an electro-responsive device connected thereto, and means for protecting said device from excessive potentials in said line, comprising an electromagnetic device in shunt to said electroresponsive device across said line, and having a magnetic circuit, the reluctance of which is responsive to increases in the potentials impressed on said electromagnetic device above a predetermined value to effectivelyv lower the impedance of said electromagnetic device whereby said electro-responsive device is effectively short-circuited for line potentials in excess of said predetermined value.

2. in combination, a line, an electro-responsive device connected thereto, and electromagnetic means for protecting said device from excessive potentials in said line, saidprotecting means comprising an inductive winding in shunt to said electro-responsive device across said line, a magnetic circuit therefor, said magnetic circuit being such as to have increased reluctance for potentials exceeding a predetermined value impressed on said Winding so as to effectively reduce the impedance of said winding tor the increased potentials, whereby said electro-responsive device is efiectively short-circuited for line potentials in excess of said predetermined value.

3. The combination with a circuit and a responsive device connected thereto, of a protective transformer having a primary winding connected in shunt to said circuit, a magnetic core section having ashort-circuited secondary winding inductively related to said primary winding, and means for bypassing the flux produced by the current in 1 said primary winding around said core section, said means being inoperative to carry additional flux when the magnetizing force produced by the current in said primary winding exceeds a predetermined value.

4:. The combination with a circuit and a responsive device connected thereto, or a protective transformer having a primary winding connected in shunt to said circuit, a core section having a short-circuited second terial the reluctance of which is much less than that ol the material of said first-mentioned core section for comparatively small magnetizing forces and is much greater for comparatively large magnetizing forces.

6. The combination with a circuit and'a responsive device connected thereto, oil a protective transformer having a primary winding connected in shunt to said circuit, a magnetic circuit for said transformer comprising two parallel core sections forming paths for the dun produced by the current in said primary winding, an cuited secondary winding on one of said core sections and inductively related to said primary winding, the other of said core sections comprising a magnetic material having a reluctance which is much less than that of the material of said first-mentioned core sec tion for comparatively small magnetizing forces and is much greater for comparatively large magnetizing forces.

7. in a protective device, a magnetic core member comprising two. core sections forming a closed magnetic. circuit, a primary Winding on one oi said core sections adapted to be connected across a circuit to be protected from excess voltages, a short-circuited secondary winding on the second core section, and a third core section connected in shunt to said second core section and comprising a' magnetic material, the reluctance of which is much less than that ol the material of said second core section for comparatively small magnetizing forces and is much greater for comparatively large magnetizing forces.

8. In a protective device, a maetic core section including a primary winding adapted to be connected across a circuit to be pro-. tected from excess voltages, a second mag netic core section including a short-circuited secondary Winding inductively related to said primary winding, and a magnetic core section in shunt to said second core section and comprising an alloy consisting chiefly of iron and nickel having a higher permeability than that of the material of said second core section at low magnetizing forces.

'9. ln a protective device, a magnetic core member comprising two core sections ot a short-cirllllll silicon steel forming a clesefi me etic cir cuit a primary winding on one 0* said core sectlons adapted to be connected. acress a circuit to be rotected from excess voliages, a short-circuited sebondary winding 0n the second core section, and a, third ewe sectien in shunt to said second core section M16 commamm prising an alloy 01' iron ami nickel in which the nickel is substantially 78 of the Whole, 10 In Witness whereof, I hereunto subscribe my name this day of February, A. 1).,

, FRANK Eu FIELD. 

